Unicortical path detection for a surgical depth measurement system

ABSTRACT

Unicortical path detection for a measurement system for monitoring a depth of penetration of a working portion of an instrument in a bone of a patient. The unicortical detection may compare an average cortex thickness in a bicortical path to an actual measured depth of penetration. If the actual depth of penetration exceeds the average thickness, a unicortical path may be detected. Upon detection of a unicortical path, an alert may be provided and/or the instrument may be arrested upon subsequent breaching of the cortex.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 62/247,025 filed Oct. 27, 2015, entitled “UNICORTAL PATHDETECTION FOR A SURGICAL DEPTH MEASUREMENT SYSTEM,” which isincorporated herein by reference in its entirety.

FIELD

The present disclosure relates to instruments for use in surgicaloperations, namely operations relative to a bone of the patient.

BACKGROUND

Systems have been proposed that may determine when a leading edge of aworking portion of an instrument is advanced from a first medium to asecond medium. Such systems may utilize sensors to monitor conditionsassociated with the advancement of the working portion to automaticallydetermine when the leading edge passes from the first medium to thesecond medium. For example, U.S. Pat. No. 6,665,948, which isincorporated by reference herein, describes one such system.

SUMMARY

In view of the foregoing, it has presently been recognized thatadditional safety measures may be utilized in conjunction withmeasurement systems that monitor advancement of a working portion of aninstrument relative to anatomy of a patient. For instance, a measurementsystem may determine when the leading edge of the working portion of aninstrument passes from a first medium to a second medium. The firstmedium may have a first density greater than a second medium having asecond density. In turn, monitoring of the leading edge as it passesfrom a first medium to a second medium may be utilized to determine theposition of the working portion as it is advanced through a bone of thepatient (e.g., with respect to the various anatomical structures of abone). In this regard, operation of the instrument and/or measurementsystem may depend upon whether the working portion is to follow aunicortical or bicortical path through a bone.

Specifically, when following a unicortical path, an instrument may bearrested or an alert may be generated upon the first occurrence of theleading edge of the working portion of the instrument passing from thefirst medium to the second medium. In contrast, when following abicortical path, the leading edge of the working portion of theinstrument may pass from a first portion of the hard outer cortex of thebone into an inner medullary layer (i.e., a first occurrence of theleading edge passing from a first medium having a higher density than asecond medium), from the inner medullary layer into a second portion ofthe hard outer cortex, and then passing from the second portion of thehard outer cortex to the exterior of the bone (i.e., a second occurrenceof the leading edge passing from a first medium having a higher densitythan a second medium).

Such a measurement system that monitors the advancement of a workingportion of an instrument may be used in a number of contexts. Forinstance, the measurement system may be used to capture of the depth ofthe path that the working portion has traveled when passing through thebone. In other approaches, the occurrence may be used to arrest theinstrument. In this approach, the instrument may be stopped to preventthe working portion from causing damage to anatomic structures exteriorto the bone once the working portion has passed through the bone. Thatis, if the instrument is not stopped once it has passed entirely throughthe bone, the working portion may damage surrounding structures adjacentto the bone. In any regard, it may be necessary to accurately determinewhen the working portion has passed through the bone.

However, in the proposed approaches, a surgeon may determine whether aunicortical or bicortical path is to be followed. However, the pathactually followed may be different than that anticipated by the surgeonor set in the measurement system. That is, the working portion mayactually follow an unintended path that may differ from the operationalmode of the instrument. For instance, where the instrument is operatingin a bicortical mode, yet the actual path of the working portion takes aunicortical path (e.g., due to misalignment of the working portion,etc.), sensing the working portion pass from the first medium to thesecond medium at the first occurrence may not result in any arresting oralerting in the instrument. That is, in normal bicortical operation thisfirst occurrence may correspond to the passing from the hard outercortex to the inner medullary layer such that normally no action istaken. However, if the actual path followed is a unicortical path, thisfirst occurrence of the working portion passing from the first medium tothe second medium may actually correspond to the working portionbreaching the exterior of the bone such that continued operation of theinstrument once the working portion passes from the first medium to thesecond medium (i.e., from the hard outer cortex to the exterior of thebone) may result in unintended operation of the instrument.

As such, the present disclosure describes unicortical path detectionthat may be used to determine that an inadvertent unicortical path hasbeen taken. In turn, bicortical operation may be overridden and an alertand/or arresting of the instrument may occur in the case of inadvertentunicortical operation. This may provide a safeguard in instances whereinstrument alignment may be difficult or other conditions exist where anintended bicortical path is actually unicortical.

Specifically, the present disclosure involves an average cortexthickness value. Specifically, the average cortex thickness value may bea predetermined value that is stored in memory and accessible by acontroller of an instrument employing a measurement system. In turn, thecontroller may monitor a depth of penetration of the leading edge of aworking portion and compare the measured depth to the average corticalthickness value. If the actual measured depth exceeds the averagecortical thickness value, the controller may alert the user and/orarrest the instrument at the first occurrence of the leading edgepassing from a first medium into a second medium having a lower densitythan the first medium. That is, the controller may override thebicortical operation of the instrument if the actual measured depth ofpenetration exceeds the average cortex thickness value.

In an embodiment described herein, the average cortex thickness valuemay be correlated to a bone type. For instance, different bone types mayhave different respective average cortex thicknesses. As such, differentpredetermined average cortex thickness values may be provided incorresponding relation to different bone types. Prior to initiatingoperation of the instrument, a bone type selection may be used toindicate the type of bone with which the instrument is to be used. Inturn, a corresponding average cortex thickness value may be retrievedfor the bone type selected and used to determine if an inadvertentunicortical path is taken. As such, variations in average corticalthickness in various bone types may be accounted for as potential forinadvertent unicortical operation may exist in a variety of bone types.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross sectional view of a bone of a patient where abicortical path is defined.

FIG. 1B is a cross sectional view of a bone of a patient where aunicortical path is defined.

FIG. 2 is a schematic view of an embodiment of a system for unicorticaldetection.

DETAILED DESCRIPTION

The following description is not intended to limit the invention to theforms disclosed herein. Consequently, variations and modificationscommensurate with the following teachings, skill and knowledge of therelevant art, are within the scope of the present invention. Theembodiments described herein are further intended to explain modes knownof practicing the invention and to enable others skilled in the art toutilize the invention in such, or other embodiments and with variousmodifications required by the particular applications(s) or use(s) ofthe present invention.

As shown in FIGS. 1A and 1B, the bony structure of the human anatomyconsists mainly of cortical bone 10 having a hard outer cortex 12 and asoft inner medullary layer 14. As shown in FIG. 1A, when advancing aworking portion 16 of an instrument on a bicortical path 18 through thecortical bone 10, the working portion 16 passes through a first portion12 a of the hard outer cortex 12, a soft non-resistant medullary layer14, and a second portion 12 b of the hard outer cortex 12.

As shown in FIG. 1B, when using a working portion 16 to advance on aunicortical path 20 through the cortical bone 10, the working portion 16passes through an entry point 22 a of the hard outer cortex 12 and anexit point 22 b of the hard outer cortex 12 without penetrating the softnon-resistant medullary layer 14.

Given that an instrument working portion 16 may pass through differentstructures depending upon whether traveling on a unicortical path or abicortical path, an instrument having a measurement system may havedifferent logic for determining when the working portion of theinstrument has passed through the bone. For example, U.S. Pat. No.6,665,948, which is incorporated by reference above, includes a modeselection switch that allows for operation in a unicortical or abicortical mode. In unicortical mode, the first occurrence of theinstrument working portion 16 passing from a first medium having a firstdensity to a second medium having a second density less than the firstdensity may trigger the output of a signal indicative that the bone hasbeen completely passed through. That is, the first occurrence of whenthe working portion 16 passes from the first medium to the second mediummay correspond to the working portion 16 exiting the cortex at the exitpoint 22 b of the bone.

However, in bicortical operation, the second occurrence of adetermination that the working portion 16 has passed from a first mediumhaving a first density greater than the second density may be used togenerate a signal indicative that the bone has been completely passedthrough. That is, the first occurrence may occur when the workingportion 16 passes from the first portion of cortex 12 a into themedullary layer 14. As such, the instrument may continue to operatebeyond the first occurrence. In turn, if the actual operation differsthan the mode selected, disregarding the first occurrence may cause thedisadvantages described above.

While the '948 Patent describes use of a force sensor and a displacementsensor for determining when the working portion 16 passes from a firstmedium to a second medium, the disclosure presented herein may beutilized with any manner of such cortical edge detection. For instance,U.S. application Ser. No. 14/845,602, which is incorporated by referenceherein, discloses use of a single sensor (e.g., a displacement sensoralone or an accelerometer alone) to determine displacement, velocity,and acceleration signals that may in turn be used to determine corticaledges. The present application may also be used in this context.Furthermore, any appropriate processing used to determine when acortical edge has been breached may benefit from use of an approach asdescribed herein.

Specifically, it may be appreciated that the potential exists for aunicortical path to be taken during operation in a bicortical mode. Sucha deviation from the intended path may result from misalignment of theworking portion, which may occur due to difficult positioning of workingportion due to anatomy or other considerations. Other times, the bonemay be relatively small such that aligning the working portion forbicortical operation is difficult to achieve. In any regard, in the casewhere a unicortical path is taken during bicortical operation of theinstrument, an incorrect or incomplete depth measurement process mayoccur or the instrument may not be properly arrested upon penetration ofthe cortex such that adjunct tissue may be damaged.

With reference to FIG. 2, a system 100 is depicted that may be used todetect unintentional unicortical operation. The system 100 includes aninstrument 20 for powering a working portion 16. As described above, theworking portion 16 may be advanceable into a bone 10 of a patient. Theinstrument 20 may be a drill, saw, reamer, grinder, pin driver, or anyother appropriate instrument for powering a corresponding workingportion 16. As such, the working portion 16 may be drill bit, pin, wire,saw, reamer, grinding burr, or any other appropriate working portion 16used in surgical operations.

The instrument 20 may be in operative communication with a measurementsystem 30. As described above, the measurement system 30 may be anyappropriate system that may be used to determine when the workingportion 16 passes from a first medium having a first density to a secondmedium having a second density. For example, the measurement system 30may be used to sense when the working portion 16 passes from a portionof hard cortex 12 a to an inner medullary layer 14 and/or when theworking portion 16 passes from the hard cortex 12 to an exteriormaterial surrounding the bone 10.

The measurement system 30 may have a controller 32. The controller 32may be used to command operation of the measurement system 30. In thisregard, the controller 32 may include a processor that is operative toaccess a memory storing machine readable instructions for configurationof the processor to achieve the functionality described herein. Thecontroller 32 may include a user interface having a display and/or inputdevices operative to display information to a user and receive inputsfrom the user. As such, operational status information of the instrument20 or measurement system 30 may be displayed to the user. For example,alarms may be displayed to the user. Moreover, control outputs forcontrolling operation of the instrument 20 or measurement system 30 maybe provided from the controller 32. For instance, the controller 32 mayoutput an alarm upon detection of a unicortical path during bicorticaloperation of the instrument 20. Moreover, the controller 32 may controlthe instrument 20 to arrest the instrument 20. This may occur when aunicortical path is detected or may occur when the measurement system 30detects the working portion 16 has passed from a first medium to asecond medium after detecting a unicortical path (e.g., once the workinginstrument 16 breaches the cortex 12).

As shown in FIG. 2, the system 100 may include a unicortical detectionmodule 40. The unicortical detection module 40 may be in operativecommunication with the measurement system 30. Regardless of the specificapproach used to monitor the working portion 16, the unicorticaldetection module 40 may interface with a displacement sensor of themeasurement system 30 to determine an actual depth of penetration of theworking portion 16 into the bone 10. As may be appreciated with furtherreview of FIG. 1, the thickness of the first portion of hard cortex 12 ain a bicortical path 18 may be less than the thickness of hard cortex 12that the working portion 16 passes through in a unicortical path 20.That is, if the instrument working portion 16 progresses on aunicortical path 20, the distance the working portion 16 travels throughthe cortex 12 may be greater than the thickness of the first portion ofhard cortex 12 a though which the working portion 16 would pass in abicortical path 18.

Accordingly, the unicortical detection module 40 may also be inoperative communication with a datastore 42. The datastore 42 may storea predetermined average cortex thickness value. The average cortexthickness value may correspond to an average thickness of the firstportion 12 a of the cortex of a bicortical path 18. In turn, theunicortical detection module 40 may retrieve the average cortexthickness value for the bone 10 and compare the depth of penetration ofthe working portion 16 into the bone to the average cortex thicknessvalue. If the actual depth of penetration of the working portion 16exceeds the predetermined average cortex thickness value, a unicorticalpath may be detected and the controller 32 may control operation of theinstrument 10 as described above. The predetermined average cortexthickness value may be slightly greater than an actual average value,thus allowing for factoring some bones with unusually thick cortices.Moreover, the unicortical detection module 40 may only detectunicortical operation if the actual depth of penetration exceeds thepredetermined average cortex thickness value by a given value (e.g., 10%of the average thickness value).

Moreover, it may be appreciated that the average cortex thickness valuemay vary with different bone types. Accordingly, the datastore 42 maystore average cortex thickness values for a plurality of bone types. Inturn, the controller 32 may include a selection presented to a user thatallows the user to indicate the type of bone in which the workingportion 16 is to be advanced. Using the indication of bone type providedby the user, the unicortical detection module 40 may retrieve acorresponding given one of the predetermined average cortex thicknessvalues for use in comparison to the depth of penetration for determiningwhether a unicortical path 20 is detected. For instance, a plurality ofbone types may be selectable via the user interface of the controller 32that each have a corresponding predetermined average cortex thicknessvalue in the datastore 42. The bone types may include a femur/tibiatype, a humerus type, a fibula type, a radius/ulna type, a pedicle type,a metacarpal/metatarsal/carpal/tarsal type, a phalanges type, a clavicletype. In addition to the selection of a bone type with a correspondingpredetermined average cortex thickness value, the controller 32 may beable to accept an average cortex thickness value from a user prior tocommencing operation.

As stated above, upon detection of a unicortical path 18, theunicortical detection module 40 may output an alarm and/or arrest theinstrument at either the time the detection occurs or at the nextsubsequent occurrence of the working portion 16 passing from a firstmedium into a second medium. The controller 32 may also have thecapability to override the alarm and/or arresting of the instrument 10.For example, after alarming/arresting, the user may determine that it issafe to continue with the operation of the instrument 10 and overridethe alarm/arresting to allow for continued operation of the instrument10.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and description isto be considered as exemplary and not restrictive in character. Forexample, certain embodiments described hereinabove may be combinablewith other described embodiments and/or arranged in other ways (e.g.,process elements may be performed in other sequences). Accordingly, itshould be understood that only the preferred embodiment and variantsthereof have been shown and described and that all changes andmodifications that come within the spirit of the invention are desiredto be protected.

What is claimed is:
 1. A measurement system for use with an instrumenthaving a working portion advanced into a bone of a patient, comprising:a depth sensor outputting a depth signal representative of adisplacement, with respect to a reference point, of a leading edge ofthe working portion into the bone of the patient; a force sensoroutputting a force signal representative of a force applied to theleading edge of the working portion axially in a direction correspondingto a working axis of the instrument; a controller comprising a processorthat is operative to access a memory storing machine readableinstructions for configuration of the processor to: communicate with thedepth sensor and the force sensor to output an alert signal indicativeof the leading edge of the working portion passing from a first mediumhaving a first density to a second medium having a second density; andexecute a unicortical detection module to compare the depth signalrepresentative of the displacement of the working portion to apredetermined average cortex thickness value such that if the depthsignal is greater than the predetermined average cortex thickness value,the unicortical detection module is operative to output an arrestingsignal to arrest the instrument upon detection of the working portionpassing from the first medium to the second medium.
 2. The measurementsystem of claim 1, wherein the depth sensor comprises a depth sensingarm engageable with a bushing disposed about the working portion.
 3. Themeasurement system of claim 1, further comprising: a user interfaceoperative to display information to a user and receive an input from auser, wherein the user interface is operative to receive a selection ofa bone type, and wherein the bone type is associated with thepredetermined average cortex thickness value.
 4. The measurement systemof claim 3, further comprising: a memory storing a data store comprisinga plurality of average cortex thickness values associated with differentreceptive ones of a plurality of bone types.
 5. The measurement systemof claim 4, wherein the unicortical detection module is operative toaccess the memory to obtain the average cortex thickness valuecorresponding to the selection of the bone type received via the userinterface.
 6. The measurement system of claim 3, wherein the userinterface is operative to present an alarm to the user that the depthsignal is greater than the predetermined average cortex thickness value.7. The measurement system of claim 1, wherein the unicortical detectionmodule does not output the arresting signal if an occurrence of theleading edge of the working portion passing from the first medium to thesecond medium occurs when the depth signal is less than thepredetermined average cortex thickness value.